1. Field of the Invention
The present invention generally relates to light valve projectors of the Schieren dark field type exhibiting greater efficiencies than prior art projectors of this type and, more particularly, to an improved light valve bar plate configuration where there is full utilization of the slots which are available in the input and output bar plates. The present invention is a new optical arrangement for light valves which may be described as "intermediate homogenized bars" that leads to much higher light efficiencies.
2. Description of the Prior Art
The general principles and mechanisms of light valve projectors utilizing Schlieren projection lenses are taught, for example, in U.S. Pat. No. 3,437,764 to Good et al. Such systems have been in use for many years and are capable of providing good performance; however, in prior art light projectors, the efficiency of the transmission of light through the input lenticular lens and bar plate is limited to about 75% of that which is possible.
In light valve projector systems, the input bar plate passes filtered light focussed onto the slots of the bar plate by a lenticular lens system composed of arrays of lenslets. The output bar plate blocks or passes light according to whether it has been diffracted by diffraction gratings written in a control layer by an electron beam. The configurations of the input and output bar plates are complementary; that is, opaque areas of the output bar plate are aligned with transparent areas of the input bar plate while transparent areas of the output bar plate are aligned with opaque areas of the input bar plate. The configuration of the input bar plate dictates the configuration of the color filter plate and the lenticular lens system.
Briefly, with reference to FIG. 1, the slots of input bar plate 18 are arranged such that the horizontally oriented slots, referred to as "green slots", are in the center of the plate and the vertically oriented slots, referred to as "magenta (red +blue) slots", are located above and below the green slots. As mentioned, the output bar plate 30 is complementary to the input bar plate; i.e., the opaque bars in plate 30 are aligned with the slots in plate 18. An enlarged view of the prior art input bar plate is shown in FIG. 2 where, for purposes of illustration, a portion of the bar plate 18 is shown broken away to reveal arrays of lenslets 55 of the lenticular lens system 28. In this type of bar plate, half of the potential green lenslets are blocked in order to obtain slot-to-slot spacing which will give good green vertical resolution. As will be observed in FIG. 2, a horizontal slot 51 is aligned with every other row of lenslets and the intervening focussed light from alternating rows of lenslets is blocked by a horizontal bar 50.
The arrangement shown in FIG. 1 is typical for light valve projectors described by Good et al in U.S. Pat. No. 3,437,764, and the invention will be described in terms of this example. It should be understood, however, that the two optical bandpass filters on plate 26 of FIG. 1 may be chosen to transmit other than green and magenta light for special applications. Moreover, the ratios of the colors, e.g. as defined by the green slots and the magenta slots, will vary depending on the chosen light source. For example, in the case of a full color television light projection system with a Xenon light source, it has been found that a ratio of 33% green and 67% magenta pupil area provides good white light balance for the light output of the projector. On the other hand, a system using a multivapor light source may require a ratio of 25% green and 75% magenta pupil area to provide good white light balance. Thus, it will be appreciated that the design details used in the description of the invention are by way of illustration only.